BASIC ?'s for DOHC CAM Adjustments

[tfrentz]

Manual Link: http://creativeconceptcomputers.com/CB750/dohc7983fck

QUESTIONS LEFT TO ANSWER:

 
?1. IN STEP #2 .... how tight do you tighten the tensioner bolt while rotating the crankshaft?

?2. IN STEP #3 .... how crucial is it that you tighten BOTH nuts AT THE SAME TIME on the rear while rotating the CRANKSHAFT? (trying to avoid needing extra hands)

?3. AT the end of the manual directions ... WHY DOES it state "WHEN THE front tensioner is loosened, the tensioners will provide the right tension"???????  Is in implying that you repeat the process again in the front for the final step????


1980 CB 750 HONDA MOTORCYCLE

Problem: Engine Ticking

Solution:

#1. Tighten Cam Chain Tensioner p.374 section 25-20 of manual
The tensioners automatically adjust after the bolts are loose so you want tension on the cam chains to ensure they're tight. Spin it by hand to maintain that tension.


STEP 1.
Level bike on center stand! Remove AC generator cover with arrow in picture below.


STEP 2.
Loosen FRONT CAM Chain lock nut and bolt. Then tighten the bolt while rotating the crankshaft clockwise and then tighten the nut.


STEP 3.
Loosen BOTH the top and bottom REAR tensioner lock nuts. TIGHTEN them WHILE ROTATING THE CRANKSHAFT clockwise.

STEP 4.
Put the AC Generator cap back on and the points/crankshaft cover.


REPAIR MANUAL ONLINE: (message me if you just want 1 section and I will email it to you!)

http://creativeconceptcomputers.com/CB750/dohc7983fck

Diagram Schematics:

http://www.cmsnl.com/honda-cb750c-750-custom-1980-usa_model1019/partslist/



My full note manual/guide is viewable at:
freehelpinghands.wordpressDOTcom/2012/06/16/honda-cb750-custom-1980-repair-guide/

[Re-run]

Well this link shows our manuals. They are factory manuals.
http://honda-cb750-s.456789.n3.nabble.com/NEW-Repair-manuals-April-26-2011-Updated-td685918.html

For cam chains, usually you do not remove any covers. On the sohc you do it with engine running or not. I prefer running as I feel it is more accurate. The manual will tell you running or not though.

[tfrentz]

PLEASE review my update and help answer the remaining 3 questions...  thanks all.

[Re-run]

First, the link I posted is our link to THAT creativeconcepts link. I know, I put it up. Any of us here can get it whenever they want.

Second, once the spring sets the tension, you tighten the bolts.
You idle the motor, loosen the front chain, there is a nut you loosen then then the bolt. Basically once the bolt is loose, wait a couple seconds and retighten it and then the nut. Repeat for the rear. Done.
The FSM only shows 1 bolt for both front and rear.

We got it covered.

[Rodgil]

On the DOHC you can adjust the cam chain tensioners while idling the motor, or by taking off a side cover and turning the motor with a spanner on the end of the crankshaft. There is a bolt and locknut on the front of the motor, between number 2 and 3 exhaust pipes. Loosen the locknut, tighten the bolt firmly, but not too hard, and tighten the locknut.  On the rear of the cylinders there are two domed 10mm nuts, one above the other, between cyls 2 and 3. Some manuals only mention one, but there are two. Loosen both and retighten (not too hard or they will strip). The rear nuts are difficult to get at, so are often not done by previous owners. I have found a 10mm ratchet ring spanner was the only way to do mine. Also, if doing with the motor running, do with a cold motor, to avoid burns. You can also loosen the nuts before starting the motor, which gives you more time to tighten, before it gets too hot. Hope this helps you.

[Re-run]

The shop manual only mentions 1 for the rear, though it is a crappy picture. I guess I am a believer in doing it with motor running. On the sohc, it started off with motor not running but then later years did it while running. Less change to mess it up I feel.

[seestheday]

For the DOHC's, there is different information in the addendum's.

For the 79-80, it says to do it with the engine running and only shows to loosen the one rear lock nut at the back (the one on the bottom).

For the 81 (my bike) the addendum says to do it with the bike cold, and manually turning the crankshaft by turning the bolt under the AC generator cover.  It also says to loosen both lock nuts on the back of the engine.

This is on page 374 of the DOHC FSM.

The FSM states "Tighten the lock nuts while rotating the crankshaft clockwise".  

So to answer the OP's questions:

1. I don't know how this is possible alone.  I did it with a friend.  
2. I don't think you need to do them both at the same time, not sure how that would even be possible/practical
3. The tensioners provide the right tension when loosened because of how they're designed.  It's essentially a spring.  The bolts just lock it in place.  

[tfrentz]

THANKS GENTS!

STEP 1.
Level bike on center stand! Remove AC generator cover with arrow in picture below.

(I was wondering WHY the AC generator cover was to be removed... "seestheDay" states that this AC GENERATOR bolt will turn the crankshaft. I had not read this anywhere else.. I had read you would turn the crankshaft by removing the points cover on the right side for SOHC and assumed it was the same. This is a helpful point "sees" is addressing. Hope this helps clarify for future readers.)   :-)

*I will just be loosening the front tensioner while idleing cold and re-tightening. THEN kill engine and loosen the back 2. THEN IDLE again while re-tightening the back.  ANY arguments with this conclusion?

STEP 2.
Loosen FRONT CAM Chain lock nut and bolt. Then tighten the bolt while rotating the crankshaft clockwise and then tighten the nut.  (THIS CAN BE DONE WHILE IDLEING instead of turning by hand)


STEP 3.
KILL ENGINE AND Loosen BOTH the top and bottom REAR tensioner lock nuts. TIGHTEN them WHILE ROTATING THE CRANKSHAFT clockwise or while IDLEING the engine.

STEP 4.
**ONLY NEEDED IF manually turning the carnkshaft. Put the AC Generator cap back on and the points/crankshaft cover.

[tfrentz]

WILL STARTING THE ENGINE to reach idle WHILE HAVING THE TIGHTENER LOOSE....damage the chain by placing torque on a potentially slacked chain????

SHOULD the engine be IN IDLE BEFORE loosening!!!!!

[TOOLS1]

I would have it idling before loosening the tension.
TOOLS

[Re-run]

Yup idling before loosening.

[munster]

The Haynes manual says just to loosen the top bolt on the main tensioner is this correct? and I saw a mention of rotating clockwise if adjusting manually, is that looking from left side as this would make the rotor side anti-clock...many thanks for answers...I am a  newcomer to the CB750.

[tfrentz]

I haven't done a cam adj for so long and my mind is scrambled right now with some other tasks so I don't want to miss guide you without having full focus on a reply.

If you have a moment post this question on the blog for others wondering the same thing... you likely won't get a reply today but if you email me again later with the answer once you find them... I would like to update the blog with your answer as well to help clarify for others.

           

Tim Frentz

Director

Helping Hands Network

FreeHelpingHands.wordpress.com

*You can send donations via paypal or email for a bank account or mailing address

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Date: Tue, 17 Jun 2014 13:47:53 -0700
From: [hidden email]
To: [hidden email]
Subject: Re: BASIC ?'s for DOHC CAM Adjustments

The Haynes manual says just to loosen the top bolt on the main tensioner is this correct? and I saw a mention of rotating clockwise if adjusting manually, is that looking from left side as this would make the rotor side anti-clock...many thanks for answers...I am a  newcomer to the CB750.

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[shinyribs]

Hayne's, Clymer's and whatever else manuals out there are all good and well,I suppose. But nobody knows these bikes as well as Honda does. Idling,not idling,hot,cold...whatever the concern is I'd go with Honda's recommendation.

FTR, you don't have to keep the crankshaft actively spinning while doing this. Just keep tension on the wrench so that the slack is pulled out of the chain.

[munster]

That sounds the way to go, and thanks for the reply...I have just done a second rebuild and the first was due to the chain eating into the alloy pre my purchase, I had it welded but the guy left a small air hole that was pushing out oil...I have now replaced the cylinders, new chains, tensioners, rings etc and don't want a repeat